Thread tension device for sewing machines



J1me 1962 e. A. OEHLSCHLAGER EI'AL 3,04

THREAD TENSION DEVICE FOR SEWING MACHINES Filed Dec. 23, 1958 INVENTORS George A. Oehlschlager Arthur S. Meloy, Jn WITNESS Fig.5 William C. Van Ness wag/m BY &M /%%W% ATTORNEY United States Patent 3,041,008 TIREAD TENSION DEVECE FOR SEWING MACHINE George A. Oehischlager and Arthur S. Meloy, Jr., Stratford, and William C. Van Ness, Devon, Conn, assignors to The Singer Manufacturing Company, Elizabeth, N..l., a corporation of New Jersey Filed Dec. 23, 1958, Ser. No. 782,493 3 Claims. ((31. 242-155) This invention relates to thread tension devices for sewing machines, and more particularly to a rotary thread tension device.

It is an object of this invention to provide a thread tensioning device for imparting a selected frictional resistance to movement of a sewing thread independently of the qualities of the thread. In other words, the main object of the invention is to provide a sewing machine thread tensioning device which when once adjusted to impart the proper frictional resistance to one given sewing thread, will impart without adjustment substantially the same frictional resistance to various sewing threads having widely different characteristics.

Another object of this invention is to provide a rotary thread tensioning wheel having spokes offset alternately in opposite directions to define two sets of spokes each set formed with a solid peripheral rim for easy threading without the use of a thread guard.

Still another object of this invention is to provide a composite thread tensioning whee-l construction in which the parts may be made separately, assembled, and secured together quickly and easily.

With the above and other objects and advantages in view as will hereinafter appear, this invention comprises the devices, combinations and arrangements of parts hereinafter described and illustrated in the accompanying drawings of a preferred embodiment in which:

FIG. 1 represents a longitudinal cross-sectional view of a sewing machine thread tensioning device in accordance with this invention,

FIG. 2 represents an elevational view of the thread tensioning wheel as viewed from the right hand side in PEG. 1,

FIG. 3 is an enlarged cross-sectional view of the assembled thread tensioning wheel illustrated in FIG. 1,

FIG. 4 is an enlarged cross-sectional view of a portion of the thread engaging disks prior to being welded together, and

FIG. 5 is an enlarged cross-sectional view of the periphery of the thread tensioning wheel taken substantially along line 5-5 of FIG. 2 and illustrating the thread thereon.

Referring to FIG. 1 of the drawings, 11 represents an adapter formed internally with a bore 12 and a counterbore 13. Externally of the counterbore, the adapter is formed with a transverse segmental slot 14 opening onto the counterbore and with an annular groove 15. The adapter is intended to be accommodated in an aperture in a sewing machine frame, the annular groove 15 serving as a set for the end of a set screw threaded in the sewing machine frame for locking the adapter thereon. Externally of the bore 12, the adapter is of reduced diameter and is drilled and tapped radially for a set screw 16, the reduced diameter providing clearance for the head of the set screw when the adapter is applied to a sewing machine.

Seated in the bore 12 of the adapter and secured in place by the set screw 16 is the base portion 17 of a stud 18. The free extremity of the stud is formed with a longitudinal slot 19 and with external threads 29. Be-

tween the base portion 17 and the free extremity, the stud is formed with a portion 21 of larger diameter, which portion is grooved lengthwise as at 22 to provide a seat for one extremity of a check spring 23 which is confined in the space between the stud and the counterbore 12. The check spring includes a radial arm 24 extending outwardly through the segmental slot 14 in the adapter and formed with a thread engaging hook 25.

Secured on the stud against the enlarged portion 21 and fixed thereon against rotation is a cupped disk 26 formed with peripheral notches 27. Also carried on the stud 18 is a pressure plate 23 having a diameter bar 29 which extends through the longitudinal slot 19 in the stud to prevent rotation of the pressure plate relatively to the stud. The pressure plate is formed with a plurality of raised spurs 30 on the side nearest the disk 26, the spurs preferably being formed by upsetting the material of the pressure plate from the opposite side, as with a punch or the like. The pressure plate 28 is urged toward the disk 26 by a beehive spring 31 constrained on the stud 18 by a knurled nut 32 engaging the threads 20.

A thread tensioning wheel, indicated generally as MB, is rotatably arranged on the stud between the disk 26 and the pressure plate 23 with pads of frictioning material 41 arranged one at each side of the tensioning wheel. The pads 41 are preferably made of felt but may be made of leather, plastic, cork, fiber, etc. Under the pressure exerted by the beehive spring 31, the frictioning pads 41 will deform to envelop the peripheral notches 27 of the disk 26 and the raised spurs 30 of the pressure plate 28, thus effectively locking the pads 41 against rotation relatively to the stud 18. Frictional resistance to turning movement of the thread tensioning wheel will, therefore, depend solely upon the frictional forces developed between the frictioning pads 41 and the thread engaging wheel.

Referring to FIGS. 2 and 3, the thread tensioning Wheel 40 is a composite of two disks 50 and 51 preferably projection welded together to provide an integral wheel. The disk 50 adjacent its transverse axis is offset to one side of the planes containing the disk and has struck out from the offset portion a hub flange 52 extending perpendicularly across the planes containing the disk 50 to provide a snug but free fit on the stud 18. The width of the hub flange 52 minimizes canting of the tensioning wheel on the stud and thus prevents the wheel from binding on the stud. Struck into the disk 50 from one side is an annular groove 53 which produces at the opposite side of the disk, an annular raised rib or projection 54. As illustrated in FIG. 4, when the disks 50 and 51 are positioned back-to-back and clamped together under pressure, initial line contact will be made between the disks only along the projection 54. Application of a high electrical current across the disks will cause heating and welding of the disks along the projection 54. This type of welding referred to in the art as projecting welding is highly advantageous in joining thread tension disks in that warpage is minimized since the heat necessary to weld the parts results from the high electrical resistance of the initial line contact. As soon as the weld begins the area of contact increases and the electrical resistance decreases thus automatically controlling the heat. When the projection Weld is completed as indicated at 54' in FIG. 3, the projection 54 will have fused with the disk 51 and the disks, being clamped together during the welding process, will be joined in abutting relation. The disk 51 is preferably formed with a large central aperture 56 extending immediately adjacent the projection '3 54 of the disk t}, thus reducing the mass of the thread tensioning wheel and providing a low moment of inertia.

The outer periphery of each of the disks 5% and 51 is identical, that is, that portion of the disk 5t) outwardly of the raised rib 54 has the same form as does the disk 51. For convenience, therefore, the same reference characters will be applied to the outer ortions of each disk and those portions of the outer periphery of disk 51 will be indicated on the drawings with prime numbers. Each of the disks 50 and 51 is formed with a continuous outer peripheral rim flared outwardly as at 57, 57'. Inwardly of the peripheral rims, each disk is formed with an annular series of substantially trapezoidal shaped openings 58, 58', defining between adjacent openings, radial fingers 59, 59. The inner portion of each of the radial fingers 59, 59 is inclined to one side of the disk on which it is formed to provide an offset 60, 61) of from /2 to 1 times the thickness of the disks 50, 51. The outer portion of each of the fingers 59, 59' is inclined outwardly in the opposite direction such that the outer portion of the fingers traverses the plane of the disk at an angle of from 20 with respect to the plane of the disk as indicated at A in FIG. 3.

As is illustrated clearly in the enlarged cross-sectional view of FIG. 3, the inclination of the inner portion of each of the radial fingers 59, 59 to provide the oifsets 60, 60' as described above, extends from the inner diameter common to the openings 58, 58'. An advantage of this construction is that the pair of annular members which make up the thread engaging wheel will automatically orient each other in coaxial arrangement and will thus facilitate manufacture of the thread engaging wheels of this invention.

The disks 50 and 51 are assembled and secured permanently together with the radial fingers 59 of disk 50 offset in a direction opposite that of the fingers 59 of disk 51, as illustrated in FIG. 3. As shown in FIG. 2 the radial fingers of one disk are disposed opposite the openings in the other disk. Furthermore, the openings 58, 58' are preferably made approximately three times as wide as the radial fingers such that when the disks are assembled, the space between adjacent radial fingers 59, 59 is approximately equal to the width of one of the radial fingers.

It is preferable, however, that the opposite sides of each radial finger 59, 59' be parallel. The space between adjacent fingers 59, 59, therefore, tapers inwardly a slight amount.

In operation, guard members are not required for the thread tensioning wheel since the continuous peripheral I hook of the check spring. Around the thread tensioning wheel the thread will take a sinuous path weaving alternately around the radial fingers 59, 59 as illustrated in FIG. 5 so that the resistance to slippage of the thread with respect to the wheel 40 will be considerable, that is, the resistance to slippage will be far greater than the maximum possible tension that the thread can sustain. The tension or frictional resistance to movement of the thread will thus depend solely upon the frictional resistance to turning of the wheel 40 offered by the pads 41.

The stud 18 is preferably formed with an axial bore 61 in which is accommodated a tension release pin 62 which abuts the diameter bar 29 of the pressure plate and protrudes beyond the base portion 17 of the stud 18 for operative engagement with any conventional tension releasing linkage of a sewing machine. When the pin 62 is shifted to the right, as viewed in FIG. 1, the pressure plate will be carried in opposition to the spring 31 away from the cupped disk 26, and the normal force imparted to the thread tensioning wheel through the frictioning pads 41 will be relieved so as to free the tensioning wheel of frictional resistance to turning and thus release the tension on the thread.

Since the radial fingers 59, 5? are oppositely ofiset as at 6t), 65?, the thread on the wheel 4i} is prevented from wedging tightly into the juncture of the disks 5t) and 51 and, therefore, the thread cannot become jammed into the wheel but will unwind freely therefrom without the imposition of objectionable tension.

As the tension or frictional drag on the wheel is increased a thread on the wheel Will be drawn inwardly on the radial fingers 59, 59. Since the space between adjacent fingers 59, 59 tapers inwardly as a result of the sides of the fingers being parallel, the thread will not be stretched as it is drawn inwardly on the radial fingers. Although the offset or amplitude of the sinuous path of the thread will increase as the thread is drawn inwardly on the radial fingers, the space between offsets will decrease and the two length factors will balance out to preserve a substantially constant length of thread on the tension wheel regardless of the degree of tension imposed on the thread.

The tensioning device of this invention thus imposes a resistance to movement of the thread which is in complete independence of the character of the thread, and the transfer of the thread onto and from the tensioning device does not influence the tension imparted thereto.

The tensioning device, moreover, is simple and economical to produce and the composite disk construction of the thread engaging wheel provides for an extremely light and small rotating mass in which the inertia forces and consequent overthrow commonly experienced in prior art rotary tensions is minimized.

Having thus set forth the nature of the invention, what is claimed herein is:

l. A rotary thread tensioning device for a sewing machine comprising a stud adapted to be fixed on a sewing machine, a thread engaging wheel rotatably carried on said stud and having a low moment of inertia, said thread engaging wheel comprising a pair of contiguous annular members of sheet material of substantially uniform thickness, each of said annular members being formed inwardly adjacent the periphery with an annular series of openings, said openings in each of said annular members extending inwardly to points equidistant from the axes of said members, said openings defining radial fingers of rectangular cross-sectional shape on each of said members between adjacent openings, means adjacent to said points for securing said members together in continuous contiguous relation with each of said radial fingers being disposed opposite an opening in the opposing member, each of said radial fingers being formed between its ends with an offset portion extending laterally from said points toward said opposing member, said offset radial finger portions protruding completely through the opposite opening of the contiguous member, and adjustable frictioning means carried by said stud and contacting the thread engaging wheel for resisting turning of the wheel rela tively to said stud.

2. A rotary thread tensioning device as set forth in claim 1 in which the means for securing said contiguous annular members of the thread engaging wheel together comprises a continuous annular projection Weld.

3. A rotary thread tensioning device as set forth in claim 1 in Which a circular hub portion is formed concentrically on a first of said pair of annular members comprising said thread engaging wheel, the second of said pair of annular members being formed concentrically with a circular aperture having a diameter larger than said hub portion of said first annular member, and said adjustable frictioning means carried by said stud contacting only the circular hub portion of said first of said pair of annular members.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Macaulay Aug. 10, 1869 Wardwell June 5, 1900 5 Smith Mar. 30, 1943 6 Eaton et a1. Oct. 17, 1944 Fentress Sept. 6, 1949 Wentz Aug. 2, 1955 Brey Sept. 25, 1956 Zeier et a1 Oct. 22, 1957 Dunn et a1. May 24, 1960 

